Dell N3200-ON Networking N-Series Switches User Guide version 6.8.0 - Page 235

NSF and VoIP Figure 8-13 shows how NSF maintains existing voice calls during a failure of the management unit in the stack. Assume the top unit is the management unit in the stack. When the management unit in the stack fails, the call from phone A is immediately disconnected. The call from phone B continues. On the uplink, the forwarding plane removes the failed LAG member and continues using the remaining LAG member. If phone B has learned VLAN or priority parameters through LLDP-MED, it continues to use those parameters. The stack resumes sending LLDPDUs with MED TLVs once the control plane restarts. Phone B may miss an LLDPDU from the stack, but should not miss enough PDUs to revert its VLAN or priority, assuming the administrator has not reduced the LLDPDU interval or hold count. If phone B is receiving quality of service from policies installed in the hardware, those policies are retained across a restart of the management unit in the stack. Figure 8-13. NSF and VoIP Stacking 235